It was a watershed week in the history of rock. A week when the old British establishment was toppled and a new wave of American bands took over. A week when the generational divide was reasserted, and teen-pop duo Daphne and Celeste were pelted with bottles full of urine. A week when Britt Ekland slipped on a melon and broke her ankle. It was that kind of week. Nothing will ever be the same again.

It started last weekend, when the Reading and Leeds festivals, though headlined by Oasis, Stereophonics and Pulp, were dominated by the sound of nu metal: hordes of kids in baggy shorts moshed to Slipknot and Limp Bizkit and booed every mention of Oasis's name. One merchandise salesman revealed that, on Monday in Leeds, he had sold 14 Oasis T-shirts and 2,500 Slipknot T-shirts. The covers of both NME and Melody Maker featured Fred Durst of Limp Bizkit singing to a sea of faces at Reading. According to Wednesday's Independent, this was 'the night the Nineties ended'.

On Tuesday, day zero of the new era, I went to the annual awards ceremony for Kerrang! magazine - until recently an anachronistic heavy rock magazine, now the bible of the nu-metal scene and the only music magazine in Britain with rising sales figures. The magazine's editor Paul Rees hailed 'a remarkable year for rock music'. Slipknot collected three awards, each time smashing up their chairs and tossing microphone stands from the stage. An hour later, Britt Ekland had her unfortunate accident, having to be carried up on to the stage in order to present an honorary award to Marilyn Manson, last year's scariest man in the world, who praised Slipknot for their 'honesty' and mused about being 'over the hill'.

It was a bizarre evening, but the sense of being on the right side of a coup d'état was unmistakable. The Kerrang! Creativity Award, for example, went to Ross Robinson, the man who discovered and produced many of the bands at the heart of this new wave - including Slipknot - and who has just been given his own international record label by Virgin. With his bright white sneakers and clean-cut face, this 33-year-old Californian looks an unlikely revolutionary, but he talks the talk. In a booth at the Hammersmith Palais, while a succession of people come over to slap his back, Robinson explains the spirit that unites this new wave of rock bands: 'Passion and hunger,' he says. 'Absolute hunger. It's not about getting chicks or making money or any of that crap. It's about being pure and real, beautiful and extreme.'

As with punk in the Seventies, the movement is spearheaded by two bands with markedly different agendas - Limp Bizkit, the Clash-like poster boys, and Slipknot, the Sex Pistols of their generation: mask-wearing nihilists who hate everything.

Following in their slipstream are a legion of American bands, including established, million-selling acts like Korn, Kid Rock, Deftones and Rage Against the Machine, and newer bands such as Amen, Glass Jaw and At The Drive-In.

Whatever you want to call this movement - nu metal, sports metal, adidas rock -it has its roots in the fusion of hard rock and hardcore rap. The bands are all white, as are most of their fans, but they revere and borrow from the musical and fashion stylings of black hip-hop culture, creating a massive new subculture which is energetic but nihilistic, angst-ridden but with the beats and riffs to get a frat party going.

All these bands know each other, but they are not exactly friends. In the space of three days, I hear Slipknot diss Limp Bizkit, Marilyn Manson diss Limp Bizkit, and Limp Bizkit diss Slipknot and Marilyn Manson. As Fred Durst yells on Limp Bizkit's recent Top 3 single, 'Take A Look Around' (the theme to Mission Impossible 2 ), 'hate is all the world has seen lately'.

To anyone over the age of 20, there is something comical about all this. I have seen few things funnier than Slipknot's unease at the Kerrang! Awards. 'We don't know how to feel about this,' one of the masked figures confessed gruffly as he clutched the Best International Live Act gong. 'It's way too formal and we're a band that likes to puke on each other and beat each other up.' Ten minutes later, pronounced Best Band in the World, they throw a table full of drinks to the floor, dedicate the award to 'my grandmother', then stand meekly in line to collect their gold discs. The ghost of Spinal Tap hovers in the background.

But the fact that it's all been done before doesn't make this phenomenon any less meaningful. This is the sound of a generation - or at least of the half of a generation that isn't E'd off its collective head at the local club. Ecstasy and agony, it seems, are the only popular cultural options available to the modern teenager.

Twenty-four hours later, in a Parisian boardroom, angst is still in the air as Limp Bizkit's Fred Durst and Wes Borland answer questions from the European press about Woodstock (the band were blamed by some people for the rioting and arson that took place at last year's festival), the title of their forthcoming album ( Chocolate Starfish and the Hot Dog-Coloured Water - it's lavatorial humour; 'the most stupid title we could think of'), and why they think everyone hates them. 'It is just marketing, yes?' probes one French journalist. Durst and Borland are articulate and dry-witted, but their message is familiar and deadly earnest. 'I'm not drinking alcohol and popping pills and taking heroin and fucking chicks all day,' says Durst, who is 26, gruffly good-looking and permanently baseball-capped.

He is, rather, trying to express his feelings about the screwed-up nature of the world, and by extension the feelings of 'his' generation (albeit most of his generation are roughly half his age). The chorus to the band's new single, 'My Generation', goes: 'How can we give a fuck about anyone else if they don't give a fuck about us?' Outside on the street, hundreds of French skate-kids send up chants of approval.

Like Slipknot, Korn and others, Limp Bizkit's main, abiding concern is for their fans. They are in the vanguard of bands using the internet to their advantage - their latest free-entry tour of the US was sponsored by Napster - and, in contrast to the rather high-minded, artistic ways of earlier rock bands, Limp Bizkit regard themselves as their fans' servants, much as boy-bands profess to do. 'We would never have a sudden change of musical direction and leave our fans behind,' Durst swears. 'Our new album is like the first two, only more so. If you like Limp Bizkit, you'll love the new album. If you don't like us, you'll hate it.'

By 9pm a generation is sweating out its anxieties in a seething, sweltering, 2,000-capacity venue. All bare-chested boys and nose-ringed girls, the Parisian audience is in its late teens and knows every word to every noxious American rap ('Everything is fucked, everybody sucks... your best bet is to stay away, motherfucker!'). At heart, though, Limp Bizkit are a powerful, theatrical rock band - entertainers who cover George Michael's 'Faith' and use fireworks, glitter confetti and jets of flame to give things a lift. Next March's European tour will, they promise, be a production '10 times bigger than anything seen in the last few years'. Afterwards the reviewer from Kerrang! sniffs something disdainful about 'metal cabaret'.

As Durst well knows, mass success brings with it the seeds of destruction, particularly for bands as desperately, self-consciously 'real' as Limp Bizkit and Slipknot. At the Kerrang! Awards, Ross Robinson muttered darkly about nu metal already being 'about to die'. In the Paris press conference, Durst imagines, a few years down the line, that 'everyone will be like: "Limp Bizkit? They suck, man!" The best any band can hope for is to be a little moment in history.'

Fasten your seatbelts, dudes. This is your moment.

The beginner's guide to Nu Metal

The bands Limp Bizkit. Slipknot. Korn. Rage Against the Machine. Deftones. Amen. Static-X. System of a Down. At the Drive-In. Snot. Orgy.

The music Loud and heavy guitars, big crashing drums - a bit like old metal (Metallica, Anthrax etc), but with hip-hop and dance rhythms, and often with rapped vocals. No guitar solos.

The fashion Multiple piercing, sometimes with chains. Tattoos and bodypaint. Baggy shorts. Trainers. No leather, spandex or long hair.

The influences Nu metal fans are generally unaware that music existed before 1991. Their Beatles are Nirvana, Rage Against the Machine, Red Hot Chilli Peppers and Eminem.

The lyrics Angst-ridden and filled with doom and bitterness. Lots of swearing and generalised swipes at the 'system'. Very little sex, no satanism.